JPS608021A - Compression molding - Google Patents

Abstract

PURPOSE:To hold the optimum pressure at every shot in a mold and to obtain molded pieces of high precision and high quality continuously by detecting the pressure in a mold cavity and adjusting compression force to filler to comform to the pressure wave form preset in the mold. CONSTITUTION:The fixed retainer plate 2 and the movable retainer plate 3 are abutted against each other to form a cavity 4 in the mold 1. Then, the injection device 6 is driven to inject resin into the cavity 4 through the nozzle 7, the sprue 8, the runner 10, the pin gate 11. A pressure detecting pin 12 is set on the fixed plate 2, the external end is abutted against the sensor 13 for the pressure in the mold at the runner area to detect the pressure in the mold. On the other hand, the pressure detecting pin 17 is equipped on the movable retainer plate 3, whose external end is abutted against the sensor 19 for the pressure in the cavity in the movable retainer plate 18. The pressures in the mold detected by the sensors 13, 19 are compared with the wave form of the pressure in the mold preset to control compressive force by closed loop control system 20.

Description

[Detailed Description of the Invention] (IJ Technical Field of the Invention The present invention relates to a compression molding method, and more specifically, is characterized in that the compression force is adjusted based on the internal mold pressure in the mold cavity. .

(2) Prior art and its problems Molding materials, especially molten resins, undergo large material shrinkage during molding. In order to compensate for this shrinkage, in injection molding, the dimensions of the mold cavity are corrected on the mold surface, and the molten resin is compressed by holding pressure on the molding surface. In the latter case, distortion in the vicinity of the gate is not avoided by holding pressure, except for direct gates. Furthermore, even if there is sufficient pressure near the gate, the viscosity of the molten resin increases over time, causing a pressure drop in the length direction of the flow, making it impossible to apply sufficient pressure to the end of the cavity, resulting in uniform pressure. It is not possible to obtain a suitable internal mold pressure. Furthermore, in a mold structure in which the resin in the mold cavity and the resin at parts such as the shear gate solidify quickly, there is a drawback that no holding force can be applied after the gate sol. In order to eliminate the above drawbacks, an appropriate method would be to combine injection molding, which has high productivity, with compression molding, which presses not only one gate but the entire molded product at the same time.

At present, compression molding, particularly injection compression molding, is classified into two types: compression force generated by a mold clamping mechanism and compression force generated by an extrusion mechanism other than the mold clamping mechanism. As a method using a mold clamping mechanism, for example, the 017 inx method developed by Rawlinx Co., Ltd. is known. This method involves closing the mold at low pressure, opening the mold using injection pressure, and then closing the mold at high pressure after filling.

According to this, the mold opening amount is determined by injection pressure, etc.
There is a drawback that the amount of mold opening cannot be precisely controlled.

A sand inch press method using a torque mechanism manufactured by Engel and Co., Ltd. is known. This method involves injecting the torque mechanism without fully extending it, and then stretching and compressing the torque mechanism.

In addition, recently, in order to set the opening amount of the mold, a structure has been developed that uses a mechanical stopper to restrict the movement of the movable mold.

In either method, the amount of compression cannot be adjusted depending on the filling situation. As a result, in the case of insufficient filling, sufficient compressive force cannot be applied, and in the case of overfilling, there is a risk that the mold may be damaged by the compressive force.

Furthermore, as a method using an extrusion mechanism, for example, a micro mold ink method is known. In this method, a hydraulic cylinder is provided in the mold separately from the mold clamping mechanism, and the resin in the mold cavity is compressed by the force of the hydraulic cylinder. However, this requires a large hydraulic cylinder to counteract the bulging and injection pressure, and is also subject to mold structure limitations. Moreover, the opening amount of the mold depends on the injection pressure, and there is a drawback that the opening amount of the mold cannot be accurately controlled.

What should be noted here is that the filling situation already given is not uniform from shot to shot, but differs to some extent. The state of contraction of the molten resin is influenced by the above-mentioned filling state, and also depends on molding conditions such as mold temperature and oil pressure of the compression mechanism. Furthermore, these molding conditions cannot be avoided from the influence of external disturbances and are not constant every seven yokes. Therefore, it cannot be said that the state of contraction of the molten resin is constant. Even if a certain compressive force is applied without knowing the shrinkage state of the molten resin, a high degree of reproducibility of the molded product will not be achieved.

In any of the compression mechanisms described above, the compression force is applied at a constant rate, and there is no method for adjusting the compression force in immediate response to the contraction situation.

The problem then lies in how to understand the filling status and shrinkage status of the molten resin. As shown in Japanese Unexamined Patent Publication No. 52-14658, the representative of the applicant company focused on the resin pressure from the state function of plastics, and calculated this resin pressure as the continuous mold internal pressure in the resin passage section of the mold. We have succeeded in understanding it as a waveform. This mold internal pressure waveform is determined by the length of the groove provided in the resin passage of the mold.
It is expressed as the filling status and shrinkage status of the molten resin from the start of filling the molten resin to the end of holding pressure. On the other hand, the mold internal pressure detected by setting a height in the mold cavity is detected only after the cavity is filled with resin, and is expressed as the filling status and shrinkage status of molten resin in the cavity. It will be done. Therefore, changes in the shrinkage state can be understood as changes in the mold internal pressure waveform of the cavity.

(3) Purpose of the Invention The present invention has been made in view of the above-mentioned circumstances, and its purpose is to maintain the mold internal pressure of the mold cavity at an optimal state for each shot, and to The object of the present invention is to provide a compression molding method that enables continuous molding of molded products with high precision and quality.

(4) Features of the invention A feature of the present invention is to detect the mold internal pressure of the mold cavity and adjust the compressive force on the filling material to match a preset mold internal pressure waveform, thereby optimizing the mold internal pressure for each shot. The goal is to bring it into a state of

Hereinafter, the present invention will be explained based on drawings.

(5) For drawings of an embodiment of the invention" Figure is a schematic diagram showing an injection compression molding apparatus to which the present invention is applied, Figure 2 is a block diagram of a compression force adjustment control system related to mold internal pressure, and Figure 3 is a FIG. 2 is a diagram showing a mold internal pressure waveform to be set.

In the injection compression molding apparatus shown in FIG. 1, a mold 1 forms a cavity 4 inside by bringing a fixed mold plate 2 and a movable mold plate 3 into contact with each other. Resin injected from a nozzle 7 by operating an injection mechanism 6 of an injection device 5 is injected into the cavity 4 via a sprue 8, a runner 10, and a bin gate 11. The fixed mold plate 2 is provided with a pressure detection bottle 12 in a penetrating manner, and its inner end is exposed to the runner 10 and its outer end is brought into contact with a launch part type internal pressure sensor +j13 serving as a resin passage. The pressure inside the mold of the runner section serving as the resin passage section is detected by the movement of the runner section.

On the other hand, the movable die plate 3 is held by the movable die plate 14,
It is pressed toward the fixed mold plate 2 by the mold clamping ram 16 of the mold clamping mechanism 15 via the movable die plate 14.

A pressure detection bottle 17 is provided in the movable mold plate 3 in a penetrating manner, and the inner end of the bottle 17 is exposed in the cavity 4, and the outer end is provided in the movable mold plate 18 on the die plate 14 side. Compare the mold internal pressure waveform 1 with the preset mold internal pressure waveform 1,
This is a closed loop control system that feeds back control signals to the length-bore system that drives the injection mechanism 6 to mold clamping mechanism 15. As shown in the block diagram in FIG. 2, this closed-loop control system 2o includes an injection control section 20a that controls the injection mechanism 6 based on a mold internal pressure signal from a launch section mold internal pressure sensor height 13.
And the cavity mold internal pressure sensor! A compression control unit 20b that controls the mold clamping mechanism 15 based on the mold internal pressure signal from j-19.
Both circuits basically perform the same functions.

The injection control unit 20a detects the mold internal pressure Wa at the launch 10 when the resin is injected into the cavity 4, and inputs it to the comparator 22a via the amplifier 21ai, while at the same time detecting the reference mold preset in the mold internal pressure waveform setting circuit 23a. The internal pressure waveform Wa' is also applied to a comparator 22a, where it is compared with the reference internal pressure waveform Wa' for the detection type inner layer, and a difference signal Ea is outputted to the controller 24a. A control signal Ma sent from the controller 24a to the servo valve drive mechanism 26a via the amplifier 25a corresponds to the operating amount of the length valve. As a result, the servo valve is operated to apply a predetermined amount of hydraulic pressure from the hydraulic source 27a to the cylinder of the injection mechanism 6, and the control is performed so as to match the standard type internal pressure waveform Wa'.

On the other hand, in the compression control section 20b, the mold internal pressure Wb'(i1'' of the cavity 4 filled with a predetermined amount of resin is detected by the sensor 19, and is sent to the comparator 22b via the amplifier 21b, where the mold internal pressure waveform setting circuit The standard type internal pressure waveform wb' set in advance in 23b is compared with the detected type internal pressure wb, and the resulting difference signal Eb is outputted to the controller 24b.The controller 24b passes the amplifier 25b to the length-bore valve drive mechanism 26b. A signal Mb is sent, thereby operating the servo valve to apply a predetermined amount of oil pressure from the oil pressure source 27b to the cylinder of the mold clamping mechanism 15, thereby applying compressive force to the resin in the cavity.

Reference mold internal pressure waveforms Wa', Wb' and 1 are set in advance as target values in the mold internal pressure waveform setting circuits 23a and 23b of the injection and compression control units 20a and 20b, respectively. This is repeated, and the mold internal pressure waveform when the best molded product matching the set pressure value is obtained is programmed into the setting circuits 23a and 23b.

As an example, the obtained mold internal pressure waveform is expressed as time-pressure (T-P).
The relationship shown in FIG. 3 will be explained.

When resin is filled into the cavity 4 of the mold by the injection device w5 at time t1, the front of the resin flow reaches the runner 10 and is detected as the mold internal pressure, and the filling situation at the runner 1° is the mold total pressure waveform Wa of the runner section. ′ is shown as the pressure increase. In the filling process, the injection mechanism 6 is controlled so that the mold internal pressure detected in the runner section matches the mold internal pressure waveform Wa'. Similarly, the mold internal pressure waveform Wa' is
Since the point in time when the resin is filled is indicated as the peak pressure point P1, the closed loop system may be applied only to the waveform before reaching the peak pressure so as to match the waveform before reaching the peak pressure.

On the other hand, the mold internal pressure waveform Wb' in the cavity portion is detected for the first time when the cavity 4 is mostly filled with resin, and then rises rapidly and reaches the peak pressure point pi.

After that, the gate seal point P2 is reached at time t2, but ・t
During the second hour, the injection mechanism 6 is adjusted based on the mold internal pressure waveform W a' at the launch section.

Next, the cavity begins to solidify, but unless a mold clamping force or extrusion force is applied to the cavity 4, the pressure gradually decreases as shown by the dotted line (W') in the figure due to contraction caused by resin curing. This may cause sink marks and distortion. Therefore, a compressive force is actively applied to the resin in the cavity so that the mold internal pressure according to the steady mold internal pressure waveform wb' is obtained for 25 hours as shown in the figure.

When mold internal pressure waveforms Wa' and Wb' having such characteristics are obtained in the preforming process, they are set in advance in the respective setting circuits 23a and 23b.

In the above embodiment, the mold internal pressure waveform W a' at the launch portion
Since closed-loop control is performed by combining the mold pressure waveform wb in the cavity, the filling amount can be accurately set, and there is an advantage that complete molding can be performed in response to the filling situation and the shrinkage situation immediately.

(6) Another Embodiment of the Invention In the IC of the above-mentioned embodiment, control was performed based on the mold internal pressure waveform Wa' at the launch portion up to the gate seal point P2 shown in FIG. can be set arbitrarily. For example, for a mold having a forced gate seal mechanism, it is possible to adjust the compression force based on the mold internal pressure waveform wb' in the cavity after reaching the peak pressure point P1.

According to this embodiment, stress concentration from the gate at time t2 can be eliminated, and stress near the gate that occurs during the filling process can be well dispersed before the resin hardens.

(7) Another embodiment of the invention In the above embodiment, the mold internal pressure waveform Wb′ of the cavity portion
Although the compressive force based on is shown and described as being steady, the present invention is not limited thereto. Depending on the type of resin, mold structure, molding method, etc., the compression force can be arbitrarily set and controlled from the pressure rise point at tl to the end point at t4.

Further, in the above embodiments, it has been explained that the cavity is filled with resin by controlling the mold internal pressure waveform of the resin passage, but this is not intended to be limiting.

As long as the amount of filling is accurate, it can be carried out in combination with, for example, transfer molding and compression molding.

Furthermore, the present invention can be applied to molding materials other than resins.

(8) Effects of the Invention As described above, according to the present invention, the mold internal pressure of the mold cavity is detected so that it matches a preset mold internal pressure waveform.
Since it adjusts the compression force on the filling material, compression molding is possible while maintaining the mold internal pressure of the material filled in the cavity at the optimum state for each shot, allowing molded products with excellent precision and quality to be continuously produced. It becomes possible to mold.

In addition to obtaining compressive force for the resin in the cavity by mold clamping, the same effect can be obtained by providing an extrusion mechanism for compression in the movable mold plate that makes up the mold and operating this with a closed-loop control system. It is also excellent in terms of versatility as it can be applied to existing injection molding machines.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an injection compression molding apparatus applied as an embodiment of the present invention, FIG. 2 is a block diagram of a closed loop adjustment control system, and FIG. 3 is a diagram showing a standard internal pressure waveform. 1... Mold, 4... Mold cavity, 20... Closed loop control system. Patent applicant Yoshi Yoshi, patent attorney representing Technoplus Co., Ltd. 1) Haru Yoshi

Claims (1)

[Claims] [1] Detecting the mold internal pressure of the mold cavity, and adjusting the compressive force on the molding material in the mold cavity so that the variation of the mold internal pressure matches a preset mold internal pressure waveform. A compression molding method characterized by: (2) The compression molding method according to claim 1, wherein the detected mold internal pressure is compared with a preset mold internal pressure waveform, and the compression force is adjusted by a closed loop control system. (3) The compression molding method according to claim 1, wherein the preset mold internal pressure waveform is arbitrary. (4) The compression molding method according to claim 4, wherein the compression force controlled based on the mold internal pressure waveform is due to mold clamping. (5) The compression molding method according to claim 1, wherein the compression force controlled based on the mold internal pressure waveform is generated by an extrusion mechanism.